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Simple solution

Vertical

Does the truss really need to be horizontal? It would be much easier to keep it at a steady angle if it was just hanging straight down from balloon(s). You can then adjust the angle of the things on it to the horizontal.

Re: Vertical

I like this idea:

The pressing issue is the balloon(s) swelling so much that it / they block LOHA's path. Perhaps cutting the balloon tether & launch can be coordinated? Another idea is to intentionally bursting the balloon. Launch LOHAN during free fall, using girder-mounted aerodynamic surfaces or little drag chutes to stabilize its orientation. This is easiest if the girder is imagined as an arrow: add drag-inducing features to the top of the vertically hung girder, and a pointy tip at the other end

Re: Re: Vertical

Following that line of thought, perhaps it would be better to rig some sort of sensor to detect when the balloon bursts and light LOHANS fire at that exact moment. I don't know how practical that is, but if it's doable you kill two birds with one stone: you get maximum altitude and you get the balloon out of the way.

Re: Vertical

OK, probably stupid but.....

Does the rocket have to be suspended below the balloon?

Had a vision of a totally ridiculous idea with three smaller balloons close-coupled on a small frame which had a central rod rising to the launch platform mounted above the balloons. the additional lift from the three would allow a weight below to keep the rod 'vertical' and if one balloon bursts early, having the balloons close-coupled above the centre of gravity for the weight/rod/platform will keep the orientation.

Accelerometers or similar to spot if lift is lost when the first burst pops the other two.

Gives a headline option for 'Fun-bag Three' (pleased to say that although I remember the band I don't remember any of their tracks).

Re: Re: OK, probably stupid but.....

I did think of a 'halo' truss but the change in size of the balloon would be even more catastrophic as at low altitude the balloon would bulge inside the halo plus there is the problem of keeping it in place at the top of the balloon.

This was the thinking behind having a rod up past the balloons, may cause sympathetic detonation at burst but if you have calculated the gas volume correctly then you would be launching before that point (excepting a balloon failure of course).

Did a lot of work with weather balloons when I was an apprentice radar engineer so I do understand how big they get (mahoosive springs to mind) but again by using three you would need much less gas per balloon improving your burst height.

Data! we need data!Martin Gregorie

Is there any reliable data on just how big one of the balloons can get? If not, are they so expensive that you couldn't slowly inflate one with air on the ground and track how big it gets before it bursts?

It seems to me that this is essential data because the beam length needs to be at least twice the burst size of a balloon. Three times would be better if LOHAN is to have a good chance at a vertical launch without hitting one of the balloons.

Re: Re: Re: OK, probably stupid but.....

Instead of a 'halo' truss, my "hat" rocket platform be attached to a circular net with long, thin strings radiating around the balloon to connect with the cable holding the avionics etc.

The length of the strings would allow the balloon to freely expand. The weight of the avionics would provide the counter-weight to keep the net-mounted rocket platform to remain at the top of the balloon.

Re: OK, probably stupid but.....

Just a thought. If you use three balloons, and assuming they are all the same size and tethered equally, there would probably be a gap between them that might be big enough to allow a vertical launch from a platform underneath.

Would it be feasible to have some sort of mobile weight attached to a 2 way mercury switch such that when one side of the truss goes up the weight will travel up a rail of some description to the end that has the most lift, thus counteracting the lift (assuming it gets far enough before the weight is vertical)

How about...

O O

| \ / |

| \ / |

| X |

| / \ |

| / \ |

---------------

VVVVVVVV

Might lose something in formatting, but essentially connect both ends of the truss to both balloons. If one starts to rise faster than the other it will take more of the weight and slow down, keeping them in balance.

Two possible solutions

1. Sling a weight from two lines connected to each end of the truss. If one end starts to rise above the other, the weight will transfer to the line hanging from that end and rebalance it. Downside: extra weight.

2. Four balloons on a triangular truss structure. Tie one to each corner and a fourth in the middle that is connected to all three corners. Again, any imbalance will cause the central balloon to take more weight from the other two corners and rebalance it. This gives you three mid-truss points with no balloons above them.

Maybe

Probably won't work, but is there any way of just having one balloon and making the bursting of the balloon trigger the launch somehow? I guess lots of balloon guts would get in the way a bit, and it adds a bit of complexity, but to my untrained eye it looks feasible.

Paris because wasn't something similar done for PARIS, based on altitude?

Re: Maybe

One balloon, two balloons... It barely matters how many, they'd have swollen to the point where they filled 80-90% of the available sky above the rig, anyway, as far as I can see, and you're only going to get a ridiculous little spurt of extra altitudefrom any engine you use, compared to what the balloons have already provided.

Better to consolidate all your LOHANs into one, easy to manage, package.

Ridiculous spurt.

I I recall correctly, the SPB team have decided that the wimpy little E class thing they were testing is far below the power levels required, and could well be going for M class and above. Those things don't provide a ridiculous little spurt. More like a ridiculously powerful kick in the pants and several thousand feet of altitude in about five seconds from ground level. From 80,000 feet with little atmosphere in the way, who knows how high it'll go?

Re: Ridiculous spurt.

is there a reasonable you tube video demoing one of these M class to get a visual idea of thrust the launch platform will need to withstand ?

im thinking about actually using gravity to start forward momentum off at the top of a half circle track tripping the M class main engine start at the dead centre and exiting the track at a 45 or greater vertical angle like the scifi film i forget the name of right now LOL, simple and effective and you might as well use what's available to you at the great hight for free to reach flight stability speed ASAP rather than waste it.

Self balancing strings

Hi!

If you attach a string from each balloon, entering 1/3 into the truss and attached to the battery, when one balloon starts going higher than the other, the string will pull the weigth to its side, keeping the system balanced. If needed, weight displacement can be amplified with a lever.

Re: ...soon as we can get our hands on some helium.

One of these might be useful...

http://www.nwac.co.uk/products/Carp_Cracker_Pole-5514-675.html

Have a circular base section. Attach 3 balloons tethered to this base. Have the electronics in the base too for balance. Fix the bottom thick end of the pole to the circular base. The pole will then poke out above the balloons, stick launch module on top of pole, job done, vertical launch. There are then 2 questions.

1) Will weight of pole at around 800g be too much?

2) is 9.5 metres long enough, how large do the balloons get at altitude?

Re: Re: ...soon as we can get our hands on some helium.

while i remember, dont forget to order some cheap chemical heat packs for the electronic packing as they may need it to keep functioning up there, BTW you didnt said just how big the uni guys are making the rocket glider or if you hope and plan to get above the world record for beating the record for Unmanned gas balloon 53.0 km (173,900 ft) http://en.wikipedia.org/wiki/Flight_altitude_record#Unmanned_gas_balloon

I'd...

hang an octohedron by its top apex to the balloon tether and launch through one wall of that. Hang the recovery parachute from the bottom apex and put the logging equipment in the bottom half of the octohedron. Forget about launching vertically! With all that tossing, who's to say what's vertical anyway?

Wrong balloon?

Why not use a balloon that doesn't explode?

Either have a pressure relief valve, or use a large, partly filled, inelastic balloon filled with just enough helium to reach a target height. An aluminised mylar balloon should do nicely, but you'll need to glue the seams (you can weld plain mylar, but it will lose helium faster).

Re: Why not release the balloon just before ignition?

Sort-of this. one baloon pops, the truss swings down vertical. the plane swivels on the truss so it points upwards, pop the other baloon and launch along the length of it? LOHAN orbs burst, slides along truss, ejects into space.

Re: Re: How do JPA do it?

don't know about the horizontal issue, but...

...why would the two balloons need to be on long tethers that could twist around each other?

I assume that the plan is to make the girder long enough to leave a big enough space to shoot the vulture between them (ooh, err, missus!); then all you need to do is make sure the tether lines are less than the length of the girder (or maybe less) and the two balloons shouldn't get tangled.

As for the horizontal issue, I'm going with Albert G's self balancing strings dragging the gubbins around to balance it out. That and using a spring balance when filling the balloons with helium to get an approximate match on lift generated by each one before launch.

You can remove a good portion of either end of the triangular support and mount the string from the balloon near the two cameras. The upside down V of the string as shown in the diagram would be well clear of the LOS for the camera lens and you would save a few inches of material at either end. Everything else outside of the cameras could be removed easily as it does not seem to serve any purpose beyond being a mount point for the string.

Swivel mount

How about mounting LOHAN, not directly on the girder, but on a rail hung off of a swivel mount, so that LOHAN will point up vertically, regardless of whether the main girder is horizontal or not. Have to make sure that the swivel doesn't freeze up, perhaps by using kel-f surfaces, and loose tolerances (bolt size << hole size). If you want to guard against the other axis tilting, you can put in a double swivel mount...